Process for continuous hydrogenation of adiponitrile

Abstract

A process for continuous hydrogenation of adiponitrile (ADN) to hexamethylene diamine (HMD) and optionally to amninocapronitrile (ACN) involving the catalytic hydrogenation of adiponitrile at relatively low temperature (e.g., 75° C.) and pressure (e.g., 500 psig) using a sponge cobalt catalyst (Raney® Co) in a reaction medium that is substantially free of caustic. In such a process periodic addition of water controls the production of side reaction products and the periodic addition of ammonium hydroxide rejuvenates the catalyst. Hexamethylene diamine is an important intermediate for the synthesis of polyamides such as Nylon-6,6 and aminocapronitrile is a potential intermediate of Nylon-6.

We claim: 
     
       1. A process for the continuous hydrogenation of adiponitrile to hexamethylene diamine and optionally to aminocapronitrile in a reaction medium which is substantially free of caustic comprising the steps of: (i) contacting adiponitrile and hydrogen in the presence of a sponge cobalt catalyst and in a reaction medium which is substantially free of caustic at a temperature of 25 to 150° C. and at a pressure up to 2,000 psig for a time sufficient to convert at least a portion of said adiponitrile to hexamethylene diamine and optionally to aminocapronitrile;   (ii) continuously adding adiponitrile to said reaction medium;   (iii) continuously removing hexamethylene diamine and optionally aminocapronitrile from said reaction medium; and   (iv) recovering said hexamethylene diamine and optionally said aminocapronitrile.   
     
     
       2. The process of claim 1 further comprising: (i) adding water to the reaction medium when between 5 and 11 molar percent BHMT appears in the reaction product, and   (ii) discontinuing the water addition to the reaction medium when the level of BHMT in the reaction product drops below 1 molar percentage.   
     
     
       3. The process of claim 1 wherein the amount of adiponitrile supplied to the reaction medium is from 0.5 to 5.0 grams/hour per gram of catalyst. 
     
     
       4. The process of claim 3 where the sponge cobalt is modified with 0.5 to 6.0 weight % of at least one of the group consisting of nickel, chromium, iron, and molybdenum. 
     
     
       5. The process of claim 1 further comprising the step of periodically adding an effective amount of ammonium hydroxide to said reaction medium to rejuvenate said catalyst.